This invention relates to olefin polymerization. In one of its aspects this invention relates to the production of block copolymers of olefins. In another of its aspects this invention relates to a continuous process for producing block copolymers of olefins. In a preferred aspect the invention relates to producing impact-resistant block copolymers having a block of propylene homopolymer and blocks of a polymer of ethylene.
Batch polymerization processes employing a catalyst system which exhibits a relatively high productivity by employing two components with a first component prepared from materials such as titanium tetrachloride, ethyl benzoate, and magnesium chloride and a second component prepared from materials such as triethylaluminum and ethyl anisate are well known in the art. Such a catalyst system produces large quantities of solid polymer per unit of catalyst. Ser. No. 703,473, filed July 8, 1976, now U.S. Pat. No. 4,234,710 provides an improved catalyst and a process for its use by incorporating into the first component a solid organic material such as durene which is inert to the catalyst component. The incorporation of a material such as durene improves the batch polymerization process by improving the stereospecific nature of the catalyst to provide an even higher yield of usable polymer per unit of catalyst.
A continuous process for producing block copolymers having blocks of propylene homopolymer and blocks of polymers of other olefins, particularly polymers of ethylene, has now been discovered using the catalyst formerly known to be useful in batch processes in which several additional advantages accrue. Due to the reactivity of the catalyst system used, all or substantially all of the residual ethylene passing into the second reaction stage is consumed in the second reaction stage. It is not necessary, therefore, to separate ethylene from propylene in a monomer recovery zone as it would be in current processes where ethylene is polymerized in a second reactor in the presence of liquid propylene. It can be seen that such advantages can be of great importance economically. Since ethylene is polymerized rapidly with the catalyst system employed, the reactor used in the first stage of a two-stage polymerization process can be much smaller, i.e., about 10 percent of the size of the reactor of the second stage rather than approximately the same size when propylene is polymerized first. The ethylene polymer is polymerized first because the ethylene polymer segment of desirable impact-resistant block copolymers containing propylene homopolymers generally amounts to less than about 20 weight percent of the total polymer.
It is, therefore, an object of this invention to provide a continuous process for the production of polymerized products of 1-olefins in which at least two reactors are employed in a series. It is another object of the invention to provide a continuous process for the production of block copolymers in which the blocks are made up of propylene homopolymer blocks and blocks of polymers of ethylene. It is another object of this invention to provide polymers made by the process of this invention.
Other objects, aspects, and the various advantages of this invention will become apparent upon reading this specification and the appended claims.